Method and apparatus for transmitting data over a downlink channel of at least one of a plurality of cells

ABSTRACT

A method and base station are disclosed. The base station comprises a wireless transceiver and a processor. The base station performs wireless communications with a wireless transmit/receive unit (WTRU) via a primary cell, transmits a message via a shared channel of the primary cell, wherein the message includes information identifying a plurality of non-primary cells, and transmits, to the WTRU, data over a downlink channel of at least one of the plurality of non-primary cells identified by the message.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/008,178, filed Aug. 31, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/533,320 filed on Aug. 6, 2019, which issued asU.S. Pat. No. 10,764,803 on Sep. 1, 2020, which is a continuation ofU.S. patent application Ser. No. 15/212,403, filed on Jul. 18, 2016,which issued as U.S. Pat. No. 10,390,279 on Aug. 20, 2019, which is acontinuation of U.S. patent application Ser. No. 13/236,133 filed onSep. 19, 2011, which issued as U.S. Pat. No. 9,438,381 on Sep. 6, 2016,which is a continuation of U.S. patent application Ser. No. 10/925,426,filed on Aug. 25, 2004, which issued as U.S. Pat. No. 8,023,463 on Sep.20, 2011, which claims priority from U.S. Provisional Application Nos.60/497,747 filed on Aug. 25, 2003; 60/507,554 filed on Oct. 1, 2003;60/508,797 filed on Oct. 3, 2003; 60/520,207 filed on Nov. 14, 2003 and60/585,174 filed on Jul. 2, 2004, which are incorporated by reference asif fully set forth. This application is related to U.S. patentapplication Ser. No. 15/212,402, filed Jul. 18, 2016, which issued asU.S. Pat. No. 10,251,106 on Apr. 2, 2019. This application is related toco-pending U.S. Patent Application entitled “Method and Apparatus forTransmitting Data Via a Plurality of Cells ”, attorney docket numberSIG-2-0644US09, filed Nov. 16, 2020, and co-pending U.S. PatentApplication entitled “Method and Apparatus for Monitoring DownlinkChannels of a Plurality of Cells and Receiving Data Over a DownlinkChannel”, attorney docket number SIG-2-0644US10, filed Nov. 16, 2020.

FIELD OF INVENTION

The present invention is related to a wireless communications. Moreparticularly, the present invention is related to an enhanced uplink(EU) operation during a soft handover.

BACKGROUND

Cellular wireless communication networks are divided into a plurality ofcoverage regions. Each coverage region in the network is served by aNode-B. As a wireless transmit/receive unit (WTRU) travels, it may movefrom one coverage region to another in the network.

The WTRU is served by the designated Node-B for a particular coverageregion. The regions covered by Node-Bs overlap each other, and at theboundary of the region a WTRU can establish connections with more thanone Node-B. As the WTRU moves from one coverage region to another in thenetwork, the WTRU goes through handover. Soft handover is widely used toensure communication without interruption while roving around aplurality of cells.

Soft handover occurs when a WTRU is connected to two or more Node-Bssimultaneously, on the same frequency. In soft handover, all Node-Bsserving the WTRU process the received data, which is then routed to aradio network controller (RNC) for macro diversity combining. Forsimplicity, the RNC may use an error detection technique such as aCyclic Redundancy Check (CRC) and may accept a packet that passes theCRC.

Softer handover is a special case of soft handover. When a WTRU is insofter handover, the WTRU is connected to two or more cells belonging tothe same Node-B. In contrast to soft handover, in softer handover macrodiversity with or without maximum ratio combining can be performed inthe Node-B.

Automatic repeat request (ARQ) is a technique whereby the receiverrequests a retransmission of packets by the transmitter if errors aredetected. Hybrid ARQ (H-ARQ) is a technique whereby transmitted datablocks are encoded for partial error correction at the receiver, andonly data blocks with uncorrected errors are retransmitted. In priorart, i.e. in high speed downlink packet access (HSDPA), the H-ARQfunctionality is terminated and controlled by the Node-B, (a techniquecalled Node-B-controlled H-ARQ), allowing for rapid transmissions andretransmissions of erroneously received packets. This feature was bothhighly desirable and practical because H-ARQ in HSDPA was not requiredfor soft handover. This feature would be highly desirable for EU also,but problems exist because it is intended for EU (and H-ARQ) to operateduring soft handover.

One of the problems with Node-B-controlled H-ARQ in soft handover is thelink imbalance. Since the associated uplink (UL) and downlink (DL)control signaling does not benefit from the soft handover gain, it mightbe error prone and require significant power offsets. In the DLdirection, the WTRU may not be able to receive the acknowledge (ACK) ornon-acknowledge (NACK) signals from all involved Node-Bs. In the UL, notall involved Node-Bs may be able to receive the associated controlsignaling from the WTRU, which may lead to soft buffer corruption.

A soft buffer is a buffer for implementing H-ARQ in a Node-B. Datapackets received, but not acknowledged, by the Node-B are temporarilystored in the soft buffer for incremental combining. Therefore, a datapacket transmitted, but not acknowledged previously, is combined with aretransmission of the same data packet transmitted in response to NACKsignaling. Chase combining is a special case of an incrementalcombining. The soft buffer corruption causes misalignment of an H-ARQprotocol state among different Node-Bs and leads to loss of the softhandover gain. It would be desirable to achieve efficient H-ARQoperation without the problems associated with prior art systems.

Node-Bs can often make more efficient decisions and manage UL radioresources on a short-term basis better than an RNC, even if the RNCretains overall control over Node-Bs. In order for a Node-B to assign ULradio resources to WTRUs in EU operation, the Node-B must know severalWTRU-specific parameters. Under the current 3GPP standard, only the RNCcan know the WTRU-specific parameters by means of radio resource control(RRC) messages. Therefore, it is necessary to forward the information tothe Node-B for proper scheduling of radio resources in EU transmissions.

An RNC maintains an active set of cells for each WTRU in soft handover.The RNC bases its decision to add to or remove cells from the WTRU'sactive set upon measurements provided by a WTRU and a Node-B and onmanagement of available radio resources in each cell. Under the current3GPP standards, the RNC applies RRC radio bearer (RB) control proceduresto coordinate active set cells with the WTRU, and Node-B applicationpart/radio network subsystem application part (NBAP/RNSAP) radio linkprocedures to coordinate active set cells with each Node-B.

During soft handover, some information should be communicated betweennetwork entities to support EU operation. The information includes, butis not limited to, information related to an active set, informationregarding a Node-B that controls transmissions during soft handover, EUscheduling information during soft handover, and ACK/NACK statusinformation during soft handover. The current 3GPP standards do notdefine specific protocols to transfer necessary information which areimperative in operation of EU during soft handover. Therefore, it isnecessary to define a protocol for transferring WTRU-specificinformation and other EU related information among an RNC, a Node-B, anda WTRU so that a Node-B is enabled to schedule radio resources and EUconnections are handed over properly during soft handover.

SUMMARY

The present invention is related to EU operation during a soft handoverin a wireless communication system. The wireless communication systemcomprises a WTRU, at least two Node-Bs, and an RNC. In accordance withone embodiment of the present invention, for each WTRU one Node-B isdesignated as a primary Node-B and any other Node-B within the EU activeset as a non-primary Node-B. The primary Node-B controls EU operationduring soft handover including EU scheduling and H-ARQ. Soft buffercorruption is avoided by controlling H-ARQ during soft handover only bythe primary Node-B. Alternatively, an RNC may control EU operationduring soft handover including H-ARQ. In this case, an RNC generatesfinal ACK/NACK decision based on the error check results of the Node-Bs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams of the first embodiment of the presentinvention.

FIGS. 2A and 2B are diagrams of the second embodiment of the presentinvention.

FIGS. 3A and 3B are diagrams of the third embodiment of the presentinvention.

FIGS. 4A and 4B are diagrams of the fourth embodiment of the presentinvention.

FIG. 5 is a diagram showing a streamlined connection between Node-Bs andan RNC in accordance with the present invention.

FIGS. 6 and 7 are diagrams of systems for transferring ACK/NACK signalsin accordance with the present invention.

FIGS. 8A and 8B are diagrams of a system and process for softer handoverin accordance with the present invention.

FIG. 9 is a diagram for transferring WTRU-specific information amongnetwork entities in accordance with the present invention.

FIG. 10 is a diagram for transferring information during handover amongnetwork entities in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described with reference to the drawingfigures wherein like numerals represent like elements throughout.

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment, a mobile station, fixed or mobilesubscriber unit, pager, or any other type of device capable of operatingin a wireless environment. When referred to hereafter, the terminology“Node-B” includes but is not limited to a base station, site controller,access point or any other type of interfacing device in a wirelessenvironment.

FIGS. 1A and 1B are diagrams of a system 100 and a process 150 of afirst embodiment of the present invention. The WTRU 102 establishesconnections with at least two cells controlled by different Node-Bs 104a, 104 b for soft handover. Data packets transmitted from the WTRU 102are received and processed separately by at least two Node-Bs 104 a, 104b during soft handover (step 152).

One Node-B in a group of Node-Bs in an “active set” is designated as aprimary Node-B 104 a, while other Node-Bs in the active set aredesignated as non-primary Node-Bs 104 b. An RNC 106 or the WTRU 102makes this decision (step 152). If it is decided by an RNC 106, the RNC106 informs all Node-Bs 104 a, 104 b and the WTRU 102. If it is decidedby a WTRU 102, the WTRU 102 informs either all Node-Bs 104 a, 104 b orthe RNC 106 which in turn informs all the Node-Bs 104 a, 104 b.

In making a decision regarding the primary Node-B 104 a, the RNC 106 mayuse statistics, i.e. the number of successful decodings of particularWTRUs transmissions by each Node-B 104 a, 104 b, to identify the Node-B104 a, 104 b with the best UL performance. It is the performance of thebest cell controlled by a Node-B that is evaluated, not the performanceof all cells associated with a Node-B. The RNC 106 may also select theprimary Node-B 104 a by evaluating both UL performance as describedabove and DL performance as obtained from WTRU 102 measurements. The RNC106 then notifies the Node-Bs 104 a, 104 b and the WTRU 102 regardingwhich one will be the primary Node-B 104 a via Iub signaling and RRCsignaling, respectively. The WTRU 102 may also be informed of theprimary Node-B 104 a by fast layer 1 signaling from Node-B.

The primary Node-B 104 a employs incremental combining, whilenon-primary Node-Bs 104 b may or may not use incremental combining. Ifthe non-primary Node-Bs 104 b do not use incremental combining, thenon-primary Node-Bs 104 b may use simple ARQ, and may always refreshtheir buffers and not perform any combining. This scheme eliminates theproblem of soft buffer corruption in soft handover. If both a primaryNode-B 104 a and non-primary Node-Bs 104 b perform incrementalcombining, soft buffer corruption may be eliminated with a new dataindicator or a sequence number in physical control signaling sent by theWTRU 102 to inform Node-Bs 104 a, 104 b which data packet is beingtransmitted, and thereby the Node-Bs 104 a, 104 b can manage soft bufferwithout corruption.

All Node-Bs 104 a, 104 b in the active set receive a data packet fromthe WTRU 102 (step 154). Each Node-B 104 a, 104 b performs an errorcheck on the data packet and generates an indication of success orfailure in decoding the data packet (step 156). Determining whether adata packet is successfully received is performed via an error checkprocedure; such as implementing a cyclic redundancy check (CRC). Theindication of success or failure in decoding the data packet by theNode-Bs can be configured in a variety of different forms, but will bereferred to hereinafter as a CRC result, or an ACK/NACK, in allembodiments of the present invention. However, any type of errorchecking may be performed in accordance with the teachings of thepresent invention, and it should be understood that the term “CRC” or“ACK/NACK” is used only as an illustration, not as a limitation, of thepresent invention.

When a Node-B 104 a, 104 b correctly decodes the data packet asdetermined by the error check, the Node-B 104 a, 104 b transmits thedata packet to the RNC 106. If the primary Node-B 104 a derives an ACKfrom the data packet, it transmits an ACK signal to the WTRU 102 and theRNC 106 without waiting for the CRC results from non-primary Node-Bs 104b, and refreshes soft buffer (step 158). If the primary Node-B 104 aderives a NACK from the data packet, it transmits a NACK to the RNC andwaits for the final decision from the RNC or CRC results fromnon-primary Node-Bs forwarded through the RNC 106 (step 158). Theprimary Node-B 104 a may set a timer as will be explained hereinafter.The primary Node-B 104 a transmits an ACK/NACK signal to the WTRU 102 inaccordance with the final decision made by the RNC 106 or CRC resultsforwarded from non-primary Node-Bs 104 b.

Non-primary Node-Bs 104 b transmit a data packet to the RNC 106 only ifthey derive an ACK from the data packet (step 158). The RNC 106 makes anACK/NACK decision (step 160). If the RNC 106 receives at least one ACKfrom Node-Bs 104 a, 104 b, the RNC 106 makes an ACK decision, and if theRNC 106 receives no ACK from Node-Bs 104 a, 104 b within a predeterminedtime period, the RNC 106 makes a NACK decision. The RNC 106 transmits anACK/NACK decision to the primary Node-B 104 a. The RNC 106 may not sendan ACK decision to the primary Node-B 104 a when the primary Node-B 104a derives an ACK. The RNC 106 optionally transmits the ACK/NACK decisionto the non-primary Node-Bs 104 b for soft buffer management depending onthe scheme of incremental combining at the non-primary Node-Bs 104 b.

It is optional for the RNC 106 to use the packets delivered fromnon-primary Node-Bs 104 b. If the RNC 106 uses the packet fromnon-primary Node-Bs 104 b, a media access control (MAC) function of theRNC 106 performs an in-sequence delivery mechanism over all the receivedpackets from all the involved Node-Bs 104 a, 104 b. If a Radio LinkControl (RLC) layer realized an out of sequence transmission it assumesdata is lost and requests retransmission. If the RNC 106 does not usethe packets from non-primary Node-Bs 104 b, the RNC 106 processes onlythe packets received from the primary Node-B 104 a. The RNC 106 extractsand enters the data packet into the MAC level reordering buffer. Afterthe RNC MAC performs the re-sequencing process, it sends the data to theRLC layer. Missed packets are identified and notified to the WTRU 102through RLC messaging.

Optionally, a streamlined connection may be implemented in transmissionof the result of the error check between Node-Bs and an RNC. A faststreamlined connection is explained with reference to FIG. 5. Thestreamlined connection is dedicated to fast signaling between the RNC506 and the Node-Bs 504 a, 504 b, and eliminates a long delay betweenthe RNC 506 and Node-Bs 504 a, 504 b. A high speed streamlinedconnection 510 a, 510 b is established between Node-Bs 504 a, 504 b andan RNC 506. CRC results from Node-Bs 504 a, 504 b to the RNC 506 and anACK/NACK decisions from the RNC 506 to Node-Bs 504 a, 504 b aretransmitted via the streamlined connections 510 a, 510 b. No directphysical link is required between Node-Bs 504 a, 504 b. Rather, alogical channel between Node-Bs 504 a, 504 b is required. The RNC 506coordinates establishing the logical channel.

A fast streamlined connection 510 a, 510 b may be implemented inaccordance with two alternatives. In accordance with the firstalternative, two logical channels are established between an RNC 506 andtwo Node-Bs 504 a, 504 b, respectively. The RNC 506 receives H-ARQsignaling 510 b from one Node-B 504 b and processes it before forwardingit 510 a to another Node-B 504 a. The RNC 506 recognizes the status ofH-ARQ process of each Node-B 504 a, 504 b by processing the signaling.As explained above, the CRC results are processed by the RNC 506 and theRNC 506 makes a final ACK/NACK decision and transmits the ACK/NACKdecision to the Node-Bs 504 a, 504 b.

Upon reception of the first ACK from any Node-B 504 a, 504 b in the RNC506, the RNC 506 transmits ACK decision to all Node-Bs 504 a, 504 b. Inthe case that all Node-Bs 504 a, 504 b derive a NACK, it takes some timeto wait for all Node-Bs 504 a, 504 b to provide the CRC results.Therefore, optionally the RNC 506 may set a timer waiting for allNode-B's responses and if the timer expires the RNC 506 transmits a NACKto all Node-Bs 504 a, 504 b.

In accordance with the second alternative, a single logical channelbetween two Node-Bs 504 a, 504 b via an RNC 506 is established. The RNC506 receives CRC results from one Node-B 504 b and just forwards it toanother Node-B 504 a without processing it. This process is fast sincethe signaling is just routed between Node-Bs 504 a, 504 b withoutprocessing at the RNC 506. Therefore, it avoids the processing delay andprotocol delay at the RNC 506. Each Node-B 504 a, 504 b derives thefinal ACK/NACK decision based on the collected CRC results from all theinvolved Node-Bs 504 a, 504 b in the active set. If there is at leastone ACK from any Node-B, a final ACK decision will be made at eachNode-B 504 a, 504 b. Otherwise, a final decision of NACK will be made bythe Node-B 504 a, 504 b. As stated above, each Node-B 504 a, 504 bgenerates an ACK decision upon reception of the first ACK from anyNode-B 504 a, 504 b. The Node-Bs 504 a, 504 b may set a timer waitingfor an ACK from other Node-Bs 504 a, 504 b, and if the Node-Bs 504 a,504 b do not receive any ACK before the expiration of the timer, theNode-Bs 504 a, 504 b generates a NACK decision.

The streamlined connection 510 a, 510 b between Node-Bs 504 a, 504 b andan RNC 506 may be implemented in any embodiment of the present inventiondescribed herein.

With reference to FIGS. 6 and 7, signaling of the ACK/NACK decisionbetween an RNC and Node-Bs is explained. FIG. 6 shows a system 600whereby a non-primary Node-B 604 b has the same controlling RNC (CRNC)606 as the primary Node-B 604 a. In this case, the CRNC 606 sends anasynchronous ACK to the WTRU 602 via the primary Node-B 604 a.

FIG. 7 shows a system 700 whereby a non-primary Node-B 704 b has adifferent CRNC 706 b from a CRNC 706 a of the primary Node-B 704 a. Inthis case, a serving RNC (SRNC) 707 sends an asynchronous ACK to theWTRU 702 via the primary Node-B 704 a.

FIGS. 2A and 2B are diagrams of a system 200 and a process 250 of thesecond embodiment of the present invention. In this second embodiment,incremental combining is performed in each Node-B 204 a, 204 b wherebyeach Node-B 204 a, 204 b combines a previous transmission of a datapacket with a retransmission of the same data packet with or withoutincreased redundancy from the WTRU 202.

A WTRU 202 establishes connections with at least two cells controlled bydifferent Node-Bs 204 a, 204 b for soft handover, and data packetstransmitted from the WTRU 202 are received and processed separately bythe Node-Bs 204 a, 204 b (step 252). Each Node-B 204 a, 204 b performsan error check on the data packet and generates a CRC result (step 254).Each Node-B 204 a, 204 b transmits the CRC result to the RNC 206.Simultaneously, each Node-B 2041, 204 b transmits the CRC result to theWTRU 202 as well (step 256). The WTRU 202 makes a determinationregarding whether there is at least one ACK received from Node-Bs 204 a,204 b (step 258). The WTRU 202 may receive both ACK and NACK signalsfrom the Node-Bs 204 a, 204 b. If the WTRU 202 receives no ACK, itschedules retransmission of the data packet (step 264). The Node-Bs 204a, 204 b perform incremental combining of the retransmission with theprevious transmission. If the WTRU 202 receives at least one ACK fromany Node-B 204 a, 204 b, the WTRU 202 transmits the next data packet(step 262).

The RNC 206 also makes an ACK/NACK decision based on collected ACK/NACKsignals from the Node-Bs 204 a, 204 b (step 260). The RNC 206 generatesand transmits an ACK decision (step 268) if the RNC 206 receives atleast one ACK from the Node-Bs 204 a, 204 b. Otherwise, the RNC 206generates and transmits a NACK decision to the Node-Bs 204 a, 204 b(step 270). The ACK/NACK decision is transmitted to the Node-Bs 204 a,204 b. Each Node-B 204 a, 204 b refreshes its soft buffer once itreceives ACK decision from the RNC 206 (step 272). With this scheme,soft buffer corruption is eliminated.

FIGS. 3A and 3B are diagrams of a system 300 and a process 350 of athird embodiment of the present invention. The WTRU 302 establishes atleast two connections with cells controlled by different Node-Bs 304 a,304 b for soft handover. Data packets transmitted from the WTRU 302 arereceived and processed separately by at least two Node-Bs 304 a, 304 bduring soft handover (step 352). Each Node-B 304 a, 304 b performs anerror check on the data packet and generates an ACK/NACK result based onthe error check on the received data packet (step 354). A Node-Bcoordinator 308 is provided to coordinate among Node-Bs 304 a, 304 b,and between Node-Bs 304 a, 304 b and the RNC 306. Each Node-B 304 a, 604b sends the ACK/NACK result to the Node-B coordinator 308 (step 356). Inthis embodiment, a final decision on whether an ACK or a NACK istransmitted to the WTRU 302 is made by the Node-B coordinator 308. It isdetermined whether any of the involved Node-Bs 304 a, 304 b generates anACK as a result of the error check (step 358). If so, the Node-Bcoordinator 308 commands each of all the involved Node-Bs 304 a, 304 bto flush out the corresponding soft buffer and to prepare for a newtransmission, regardless of the result of the error check derived ateach Node-B 304 a, 304 b (step 360). In response, each Node-B 304 a, 304b sends an ACK to the WTRU 302 and refreshes its soft buffer (step 362).

If the results of the error check from all Node-Bs 304 a, 304 b fail,(i.e. all of the Node-Bs 304 a, 304 b generate NACKs) or a responsetimer Node-B coordinator expires, the Node-B coordinator 308 informs allof the Node-Bs 304 a, 304 b that they failed to successfully decode thetransmitted data packet and that they should prepare for retransmissionof the data packet (step 364). In response, the Node-Bs 304 a, 304 bsend an NACK to the WTRU 302 (step 366).

FIGS. 4A and 4B are diagrams of a system 400 and a process 450 of afourth embodiment of the present invention. For soft handover, a WTRU402 establishes a separate connection with at least two cells controlledby different Node-Bs 404 a, 404 b in an active set. Data packetstransmitted from the WTRU 402 are received and processed separately bythe Node-Bs 404 a, 404 b during soft handover (step 452). Each Node-B404 a, 404 b performs an error check on the received data packets andgenerates an indication of success or failure in decoding the datapacket (step 454).

Each Node-B 404 a, 404 b transmits a CRC result to the RNC 406 (step456). If the Node-B 404 a, 404 b succeeds in decoding the data packet,the Node-B 404 a, 404 b sends an ACK to the RNC 406 along with the datapacket. If the Node-B 404 a, 404 b fails in decoding the data packet,the Node-B 404 a, 404 b sends a NACK to the RNC 406. An ACK and NACK maybe sent with each data block within Iub/Iur frame protocols betweenNode-Bs 404 a, 404 b and the RNC 406. The RNC 406 makes a final ACK/NACKdecision regarding the transmission of the data packet from the errorcheck results conducted by the Node-Bs 404 a, 404 b (step 458). The RNC406 makes an ACK decision if the RNC 406 receives at least one ACK fromthe Node-Bs 404 a, 404 b. Otherwise the RNC 406 makes a NACK decision.The ACK or NACK decision made by the RNC 406 is then transmitted back tothe Node-Bs 404 a, 404 b at steps 460 and 464, respectively. Each Node-B404 a, 404 b clears its buffer upon receipt of the ACK decision from theRNC 406. All Node-Bs 404 a, 404 b transmit the same ACK or NACK signalmade by the RNC 406 to the WTRU 402 regardless of the CRC result thateach Node-B 404 a, 404 b individually derived from the data packet(steps 462 and 466). In this case, the WTRU 402 may apply maximum ratiocombining (MRC) to the received ACK/NACK feedback signals from theNode-Bs 404 a, 404 b.

The soft buffer in each Node-B 404 a, 404 b is managed according to theACK/NACK decision made by the RNC 406, regardless of the associatederror check result derived by the Node-Bs 404 a, 404 b. Consequently,the fourth embodiment of the present invention allows the RNC 406 toalign the soft buffer status in each Node-B 404 a, 404 b. Additionally,the WTRU 402 can benefit from the soft handover gain for the ACK/NACKsignaling, since identical ACK/NACK signaling is transmitted by allNode-Bs 404 a, 404 b. As such, the WTRU 402 may perform macro diversitycombining (maximum ratio combining) for ACK/NACK signaling, since theACK/NACK signals transmitted back to the WTRU 402 from all the involvedNode-Bs 404 a, 404 b are identical.

A fifth embodiment of the present invention will be explained withreference to FIG. 2A. The fifth embodiment is similar to the secondembodiment, except that Node-Bs 204 a, 204 b do not perform incrementalcombining during soft handover. A WTRU 202 establishes connections withat least two cells controlled by different Node-Bs 204 a, 204 b for softhandover. Data packets transmitted from the WTRU 202 are received andprocessed separately by at least two Node-Bs 204 a, 204 b during softhandover. Each Node-B 204 a, 204 b performs an error check on the datapacket and transmits an ACK/NACK signal to the WTRU 202. The Node-Bs 204a, 204 b send ACKs along with an identification of transmission to anRNC 206. The WTRU 202 sends a sequence of data packets andsimultaneously looks at the MAC level for an ACK from any Node-B 204 a,204 b when it is in soft handover, and only from the current Node-B whenit is not in soft handover. This method causes retransmission wheneither the time-out threshold is exceeded for an ACK or anout-of-sequence is reported by all cells. Alternatively, this embodimentmay be implemented with respect to other embodiments including the firstembodiment shown in FIG. 1A.

FIGS. 8A and 8B are diagrams of a system 800 and a process 850 forsofter handover in accordance with the present invention. During softerhandover, the WTRU 802 establishes connections with more than one cell808 which are controlled by the same Node-B 804 (step 852). EUtransmissions from the WTRU 802 are processed by each cell 808independently (step 854), and each cell 808 transmissions received fromthe WTRU 802 are processed by the Node-B 804 controlling these cells(step 856). There are two alternatives with respect to incrementalcombining of transmissions transmitted from the WTRU 802.

In accordance with the first alternative, the Node-B 804 receives datapackets from all the involved cells 808 and combines them using atechnique, such as maximum ratio combining, before performing errorcheck on the data packet. The resulting combined data packet is errorchecked at the Node-B 804.

In accordance with the second alternative, each cell 808 processes thedata packet individually determining error check on the data packetreceived from the WTRU 802. The Node-B 804 accepts the data packet thatthe error check has passed in any of the cells 808 within the activeset.

In downlink, the Node-B 804 sends messages including ACK/NACK to theWTRU 802 via all the involved cells 808 (step 858). The WTRU 802 needsto monitor all channels, preferably shared channels, from the involvedcells 808 to detect downlink messages. The number of shared channelsthat the WTRU 802 should monitor from each cell 808 may be limited, suchas up to 4 channels.

One of the cells 808 may be designated as a primary cell 808 a, whileother cells are designated as non-primary cells 808 b. The primary cell808 a sends a message on any of the downlink shared channels allocatedto the WTRU 802. The message carries a shared channel indicator fornon-primary cells 808 b. The non-primary cells 808 b send messages onthe channel indicated by the shared channel indicator. In order toimplement this scheme, there is a timing offset between the transmissionof the shared channel indicator from the primary cell 808 a and thetransmission of messages from non-primary cells 808 b. The WTRU 802first monitors all shared channels from the primary cell 808 a. Once theWTRU 802 detects that one of the shared channels carry messages to theWTRU 802, the WTRU 802 reads shared channel indicator along with thedownlink messages from the primary cell 808 a. Then, the WTRU 802receives messages from the non-primary cells 808 b indicated by theshared channel indicator. With this scheme, it is possible to lower thenumber of channels that the WTRU 802 should monitor. The WTRU 802 thencombines the messages received from all the involved cells 808 using atechnique, such as maximum ratio combining.

Alternatively, for the DL, only the primary cell 808 a may transmitmessages to the WTRU 802. The Node-B 804 transmits downlink messages viathe primary cell 808 a, while all non-primary cells 808 b switch off thedownlink signaling to the WTRU 802. With this scheme, the WTRU 802receive processing is simplified and downlink interference is reduced.

FIG. 9 is a diagram of a system 900 for transferring WTRU-specificinformation to support EU operation 912 in accordance with the presentinvention. Initially, an RNC 906 obtains WTRU-specific information froma WTRU 902 using RRC messaging 908 at the initial connection. Then, theWTRU-specific information is forwarded from the RNC 906 to a Node-B 904to be used in scheduling EU transmissions for the WTRU 902. The transferof the information from the RNC 906 to the Node-B 904 is via an Iubinterface 910, and an Iur interface if an SRNC is not the same as aCRNC. A new signaling mechanism may be utilized to transfer theinformation from the RNC 906 to the Node-B 904, or alternatively, theexisting mechanisms over Iur and Iub interfaces may be modified in orderfor the RNC 906 to forward relevant WTRU-specific information to theNode-B 904.

FIG. 10 is a diagram of a system 1000 for transferring information amongnetwork entities during soft handover in accordance with the presentinvention. During EU operation, if a WTRU 1002 needs to change theserving cell or the serving Node-B, a softer or soft handover procedureis initiated. Hereinafter, for simplicity, the present invention will beexplained only with respect to a soft handover. During soft handover,some information should be communicated between network entities tosupport EU operation. The information includes, but is not limited to,information related to an active set, information regarding a primaryNode-B if the system so designates, EU scheduling/rate information, andACK/NACK status information.

An RNC 1006 maintains an active set of cells for handover. The RNC 1006selects and removes cells in the active set based on measurementsreported from Node-Bs 1004 a, 1004 b and the WTRU 1002 and on availableradio resources. Once the RNC 1006 selects cells for the active set, theRNC 1006 sends messages to the Node-Bs 1004 a, 1004 b and the WTRU 1002to inform the selected cells for the active set to support soft handoverfor EU. The RNC 1006 also sends messages to update the active set eachtime the RNC 1006 adds or removes a cell in the active set. The messagesmay be transmitted using existing RRC and NBAP/RNSAP active setmanagement procedures or new procedures.

Either the RNC 1006 or the Node-Bs 1004 a, 1004 b and the WTRU 1002 maydesignate one Node-B as a primary Node-B 1004 a and other Node-Bs in theactive set as non-primary Node-Bs 1004 b during soft handover. Theselection of the primary Node-B 1004 a is based on UL performancemeasured and reported by each Node-B 1004 a, 1004 b and/or DLperformance measured and reported by the WTRU 1002.

During soft handover, only the primary Node-B 1004 a performs schedulingand assigning radio resources to the WTRU 1002. The primary Node-B 1004a informs the RNC 1006 of scheduled EU transmissions via Iub NBAPsignaling or within the EU frame protocol. The RNC 1006 then informsnon-primary Node-Bs 1004 b of the allocation of radio resources for EUand routing of received data. This is also signaled over NBAP or withinthe EU frame protocol. Alternatively, non-primary Node-Bs 1004 b may beinformed by Iub NBAP procedures of sets of EU physical channels for theperiod each cell is within the active subset. Each non-primary Node-B1004 b within the active set continuously receives these channelsindependent of radio resources allocation scheduled by the primaryNode-B 1004 a.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

What is claimed is:
 1. A base station comprising: a wirelesstransceiver; and a processor, wherein the wireless transceiver and theprocessor cause the base station to: perform wireless communicationswith a wireless transmit/receive unit (WTRU) via a primary cell;transmit a message via a shared channel of the primary cell, wherein themessage includes information identifying a plurality of non-primarycells; and transmit, to the WTRU, data over a downlink channel of atleast one of the plurality of non-primary cells identified by themessage.
 2. The base station of claim 1, wherein the message istransmitted over a shared downlink channel via the primary cell, andwherein the information identifying the plurality of non-primary cellsis control information.
 3. The base station of claim 2, wherein theshared downlink channel is one of a plurality of shared downlinkchannels of the primary cell.
 4. The base station of claim 1, whereinthe message further includes information identifying a plurality ofshared downlink data channels of the non-primary cell.
 5. A method ofoperating a cellular network, the cellular network including a primarycell and a non-primary cell, the method comprising: performing wirelesscommunications with a wireless transmit/receive unit (WTRU) via aprimary cell; transmitting a message via a shared channel of the primarycell, wherein the message includes information identifying a pluralityof non-primary cells; and transmitting to the WTRU data over a downlinkchannel of at least one of the plurality of non-primary cells identifiedby the message.
 6. The method of claim 5, wherein the message istransmitted over a shared downlink channel via the primary cell, andwherein the information identifying the plurality of non-primary cell iscontrol information.
 7. The method of claim 6, wherein the shareddownlink channel is one of a plurality of shared downlink channels ofthe primary cell.
 8. The method of claim 5, wherein the message furtherincludes information identifying a plurality of shared downlink datachannels of the non-primary cell.